This invention relates to a method and apparatus for breaking a hard compact material especially rock, by means of relatively incompressible fluid, such as water.
Conventional methods of rock breakage, including drill-and-blast and crushing techniques have several disadvantages.
The drill-and-blast technique has the disadvantage of noise, gases, dust and flying debris, which means that both men and machines must be evacuated from the working area. Crushing techniques require large forces to crush the rock and the tool wear is significant.
During the last decade serious attention has been given to replacing the drill-and-blast technique for tunnelling, mining and similar operations. One alternative technique involves the use of high velocity jets of water or other liquid to fracture the rock or ore body and numerous devices intended to produce pulsed or intermittent liquid jets of sufficiently high velocity to fracture even the hardest rock have been suggested. Such devices are disclosed in for example U.S. Pat. Nos. 3,521,820; 3,784,103 and 3,796,371. For hard kinds of rock the jet impinging velocity necessary to break the material is typically 2000 meters/sec. As yet, however, jet cutting techniques are still unable to compete with the traditional methods of rock breakage such as drill-and-blast in terms of advance rate, energy consumption or overall cost. Moreover serious technical problems such as the fatigue of parts subjected to pressures as high as 10 to 20 kbar and excessive operational noise remain.
A second and even older technique for fracturing the rock and for saturating soft rock formations such as coal with water for dust suppression involves drilling a hole in the rock and thereafter pressurizing the hole with water either statically or dynamically. This second technique is described in for example German Pat. No. 241,966. According to this patent water is supplied to a hole pre-drilled in the coal stope for saturating the stope until the pores in the wall of the hole are substantially water-filled. The water supply into the hole is then increased stepwise. The stope cannot absorb this suddenly supplied large water quantity and a breaking force therefore arises in the drill hole. Due to the small breaking forces which are obtainable by this technique only soft material, such as coal, can be broken.
The object of the invention to achieve a hydraulic blasting technique which makes it possible to break compact material, such as rock, by using equipment which operates at comparatively low pressures.
It is to be understood that the term "fluid" used in the claims means a relatively incompressible substance that alters its shape in response to any force, that tends to flow or to conform to the outline of its container, and that includes liquids, plastic materials and mixtures of solids and liquids capable of flow. As example of such substance can be mentioned water, lead and plasticine.